1. Field of the Invention
The present invention relates to a fire extinguishing composition formed by thickened water, and more particularly, to a highly liquid suspension of silica in water which is further thickened upon discharge.
2. Summary of the Related Art
As an extinguishing agent water has the advantages of high heat absorbing capacity and therefore favourable cooling action, a lack of toxicity, compatibility with many flammable materials, inexpensiveness and usually a good availability. It is therefore still an important fire extinguishing agent.
A known disadvantage of water as an extinguishing agent is its highly liquid nature, so that during the extinguishing process large quantities flow away unused and in part cause unnecessary water damage. Therefore only a small part of the sprayed water has its favourable extinguishing action consisting of cooling the burning material. Therefore numerous attempts have been made to improve water as a fire extinguishing agent.
Thus, for example, the addition of substances have been described, which bring about a rise in its viscosity, such as cellulose derivatives, alginates or water-soluble synthetic polymers such as polyacrylamide. Use is also made of non-flammable mineral additives to the extinguishing water, e.g. water-soluble inorganic salts or water-insoluble materials such as bentonite or attapulgite (cf. Ullmanns Enzyklopadie der Technischen Chemie, 4th edition, Vol. 11, p.569 and Ullmanns Encyclopedia of Industrial Chemistry, 5th edition, Vol. A 11, pp. 114/5).
In special cases, such as when fighting forest fires, use is e.g. made of bentonite, attapulgite and water-soluble salts as well as extinguishing water formulations mixed with alginates and which after special preparation are frequently ejected from aircraft (cf. e.g. C. E. Hardy, Chemicals for Forest Fire Fighting, 3rd edition, Boston, 1977). Due to numerous disadvantages such extinguishing agents have only proved significant for fighting forest fires and cannot be used for general purposes.
The reasons are e.g. the generally necessary high weight percentages of mineral additives in order to achieve a sufficiently high level of thickening (e.g. 10 to 20% by weight), the corrosive action of certain salts such as sulphates or chlorides, or the possibility of undesired environmental influences occurring, e.g. of fertilizing components, whose quantity application on quenching a forest fire can e.g. be a multiple per surface area of the fertilizer application in agriculture. The preparation of such thickened special extinguishing agents generally requires special apparatus and particularly this applies with respect to the mixing thereof. They can in general not be applied using conventional fire extinguishing syringes and e.g. in the case of alginate gums do not have an optimum adhering action to the surfaces following spraying, particularly under the action of heat, they frequently change their use characteristics after even a short storage period and, after drying, sometimes leave behind difficulty removable residues.
The preparation of a thickened extinguishing water without these disadvantages, particularly a non-flammable thickening agent for the water in order to improve the water extinguishing action, is therefore highly desirable. Apart from the positive effects of adhesion to surfaces, even in the case of elevated temperatures, the formation of cohesive extinguishing agent films with a particularly high water percentage and sufficiently high stability, chemical and physiological compatibility with all dead and living materials occurring during the extinguishing process, it must maintain its use properties even after prolonged storage and, if necessary, must be preparable in a rapid, inexpensive manner by mixing with ordinary water and must be appliable using conventionally available fire extinguishing equipment. At present there is no efficient fire extinguishing agent, which satisfies all these requirements.
Certain of the requisite characteristics such as a broad compatibility with living and dead material are e.g. fulfilled by amorphous silica or silicic acid, so that the latter is not only widely used as a thickening agent (cf. Ullmanns Enzyklopadie der Technischen Chemie, 4th edition, Vol. 22, p. 473; Kirk-Othmers Encyclopedia of Chemical Technology, Vol. 20, p. 778; H. Brunner, D. Schutte, Chemiker Ztg. 89, 1965, pp. 437-40; H. Fratzscher, Farbe und Lack, 75, 1969, pp. 531-538). It has a particularly marked thickening action in the form of fumed silica prepared by flame hydrolysis in non-polar liquids. In polar liquids such as water the thickening action of said silica is less pronounced, so that it is necessary to add relatively large quantities for obtaining a significant thickening action. It is as yet not known to use silicas in the form of an aqueous suspension as fire extinguishing agents. Fumed silica is only described as a pulverulent special extinguishing agent for special fire situations (EUR 0339 162 A1 or EUR 0311 006 A1). As a result of its extreme lightness, its general use as an extinguishing agent is not practicable.
If e.g. fumed silica is suspended in water, much more than 10% is necessary in order to obtain a usable thickening and this suspension also behaves in a thixotropic manner. This is a disadvantage for use with standard fire extinguishing equipment. If e.g. a 5% suspension of fumed silica in water is sprayed from different spraying means, liquids passing thinly out of the nozzles are always obtained and they run off surfaces in the same way as water. In extinguishing comparison tests on standardized fires, such unthickened silica suspensions have no better action than water.